The Dog is a caninecarnivorousmammal that has been domesticated for at least 14,000 years and perhaps for as long as 150,000 years based on recent evidence. In this time, the dog has developed into hundreds of breeds with a great degree of variation. For example, heights range from just a few inches (such as the Chihuahua) to nearly three feet (such as the Irish Wolfhound), and colors range from white to black with reds, grays, and browns also occurring in a tremendous variation of patterns. Dogs, like humans, are highly social animals and pack hunters; this similarity in their overall behavioral design accounts for their trainability, playfulness, and ability to fit into human households and social situations.

Dogs fill a variety of roles in human society. Working dogs of all kinds do traditional jobs such as herding and new jobs such as detecting contraband and helping the blind or disabled. For dogs that do not do their traditional jobs, a wide range of dog sports provide the opportunity to exhibit their natural skills. In many countries, the most common and perhaps most important role of dogs is as companions. Dogs have lived with and worked with humans in so many roles that they have earned the sobriquet "man's best friend".

Carnivore or omnivore

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Wild dogs are shot by farmers in an effort to protect livestock. Bodies are usually tied to fences as warning to other dogs

The classification as a carnivore is a conventional one and does not mean that a dog's diet should be restricted to meat alone. Unlike a true obligate carnivore, such as a cat, a dog is able to healthily digest a variety of foods including vegetables and grains, and in fact requires a large proportion of these in its diet. Wild canines typically get such nutrients from the stomach contents of their herbivorous prey, which they consume eagerly. Dogs can survive perfectly well on a reasonably carefully designed vegetarian diet, particularly if eggs and milk products are included (i.e., not a vegan diet, although with even more attention this is also possible). On the other hand, dogs are evolved to tolerate a carnivorous diet much better than humans are, and are not susceptible to many of the metabolic ills stemming from overconsumption of such foods that civilization makes possible. In addition, the experience of extremely stressful conditions such as the Iditarod race, as well as scientific studies of similar conditions, suggest that under such extreme stress, high protein diets (which implies a lot of meat consumption) help prevent damage to muscle tissue.

Dog is also a term used by breeders to specifically denote a male domestic dog. The female is known as a bitch. A young dog is called a puppy. The words pooch and poochie are generic, generally affectionate terms for a dog, as is doggy (sometimes doggie), often used by children. Many additional terms are used for dogs that are not purebred; see Terms for mixed-breed dogs. Toy dogs are so called because of their small size; similarly for Lap dogs, with the additional connotation of an affectionate attachment between human and dog.

Attributes

Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food.

Their legs are designed to propel them forward rapidly, leaping as necessary, to chase and overcome prey. Consequently, they have small, tight feet, walking on their front toes; their rear legs are fairly rigid and sturdy; the front legs are loose and flexible, with only muscle attaching them to the torso.

Dogs are dichromats and thus, by human standards, color blind.1, 2 Because the lenses of dogs' eyes are flatter than humans', they cannot see as much detail; on the other hand, their eyes are more sensitive to light and motion than humans' eyes. Some breeds, particularly the best sighthounds, have a field of vision up to 270? (compared to 100? to 120? for humans), although broad-headed breeds with their eyes set forward have a much narrower field of vision, as low as 180?.1, 2

Dogs detect sounds as low as the 20 to 70 Hz frequency range (compared to 16 to 20 Hz for humans) and as high as 70,000 to 100,000 Hz (compared to 20,000 Hz for humans)2, and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound. They can identify a sound's location much faster than can a human, and they can hear sounds up to four times the distance that humans can.

Dogs have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren. Other than the oversimplified obvious, i.e. chemical compounds that affect chemical sensors in the nose, what a dog actually detects when he is scenting is not really understood; although once a matter of debate, it now seems to be well established that dogs can distinguish two different types of scents when trailing, an air scent from some person or thing that has recently passed by, as well as a ground scent that remains detectable for a much longer period. The characteristics and behavior of these two types of scent trail would seem, after some thought, to be quite different, the air scent being intermittent but perhaps less obscured by competing scents, whereas the ground scent would be relatively permanent with respect to careful and repetitive search by the dog, but would seem to be much more contaminated with other scents. In any event, it is established by those who train tracking dogs that it is impossible to teach the dog how to track any better than it does naturally; the object instead is to motivate it properly, and teach it to maintain focus on a single track and ignore any others that might otherwise seem of greater interest to an untrained dog. An intensive search for a scent, for instance searching a ship for contraband, can actually be very fatiguing for a dog, and it must be motivated to continue this hard work for a long period of time.

All dogs have a tremendous capacity to learn complex social behavior and to interpret varied body language and sounds, and, like many predators, can react to and learn from novel situations. The requirements of coordinating complex social behavior requires that canines have the ability to sense and deliver a wide variety of cues via body language, more so than for even humans, who can use language for the same purpose. Physiologically, this correlates with such features as a large number of nerves innervating the facial muscles of dogs, allowing subtle control of a wide variety of facial expressions; in contrast to cats, for instance, who have many fewer nerves governing their facial muscles, resulting in a smaller repertoire or "vocabulary" of expressions. This ability to read and deliver nonverbal cues makes dogs expert at reading human beings, as well, often even more so than other humans are, who rely on language. Most dog owners have a large collection of stories about their dogs recognizing individuals by their footsteps outside the door, and so on.

Dog coats, colors, and markings

Coat colors range from pure white to solid black and many other variations.

For a complete detailed list of dog colors and patterns, see Coat (dog).

Dogs exhibit a diverse array of coat textures, colors, and markings, and a specialized vocabulary has evolved to describe them.

Originally, dogs all had dense fur with an undercoat and long muzzles and heads, although both of these features have been altered in some of the more extremely modified breeds, such as the Mexican Hairless and the English Bulldog.

One often refers to a specific dog first by coat color rather than by breed; for example, "a blue merle Aussie" or "a chocolate Lab". Coat colors include:

Two-color coats, such as Black and tan, red and white: Coat has both colors but in clearly defined and separated areas; usually the top and sides are darker and lower legs and underside are the lighter color.

Tricolor: Consisting of three colors; usually black, tan, and white or liver, tan, and white.

Brindle: A mixture of black with brown, tan, or gold; usually in a "tiger stripe" pattern.

Coat textures vary tremendously, so that some coats make the dogs more cuddly and others make them impervious to cold water. Densely furred breeds such as most sled dogs and Spitz types can have up to 600 hairs per inch, while fine-haired breeds such as the Yorkshire Terrier can have as few as 100, and the "hairless" breeds such as the Mexican Hairless have none on parts of their bodies. The texture of the coat often depends on the distribution and the length of the two parts of a dog's coat, its thick, warm undercoat (or down) and its, rougher somewhat weather-resistant outer coat (topcoat), also referred to as guard hairs. Breeds with soft coats often have more or longer undercoat hairs than guard hairs; rough-textured coats often have more or longer guard hairs. Textures include:

Double-coated: Having a thick, warm, short undercoat (or down) that is usually dense enough to resist penetration by water and a stronger, rougher weather-resistant outer coat (topcoat), also referred to as guard hairs. Most other coat types are also double coated.

Squirrel: Carried high and towards the head, often with the tip curving even further towards the head.

Wheel: Carried up and over the back in a broad curve, resembling a wheel.

Anatomy

Like most predatory mammals, the dog has powerful muscles, a cardiovascular system that supports both sprinting and endurance, and teeth for catching, holding, and tearing.

The dog's ancestral skeleton provided the ability to run and leap. Although selective breeding has changed the appearance of many breeds, all dogs retain the basic ingredients from their distant ancestors. Dogs have disconnected shoulder bones (absent the collar bone of the human skeleton) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and most have vestigial dewclaws on their front legs.

The dog's ancestor was about the size of a Dingo, and its skeleton took about 10 months to mature. Today's toy breeds have skeletons that mature in only a few months, while giant breeds such as the Mastiffs take 16 to 18 months for the skeleton to mature. Dwarfism has affected the proportions of some breeds' skeleton, as in the Basset Hound.

Ancestry and history of domestication

This ancient mosaic shows a large dog with a collar hunting a lion.

Molecular systematics indicate that the domestic dog is descended from a wolf-like ancestor, and dogs and wolves can still interbreed. The domestication of the dog probably occurred at least 14,000 years ago, and perhaps long before that. There is archaeological evidence of dog remains, showing the characteristic morphological differences from wolves, from at least 14,000 years ago, while wolf remains have been found in association with hominid remains that are at least 400,000 years old. The molecular genetic data suggest that the domestic lineage separated from modern wolves around 150,000 years ago (Vilࠥt al, 1997). In the early 2000s, some research (http://www.amonline.net.au/archive.cfm?id=716) indicated that domestication in fact had already begun to occur as early as 100,000 years ago.

Dogs were, and are, valued for their aid in hunting. Dog burials at the Mesolithic cemetery of Svaerdborg in Denmark indicate that, in ancient Europe, dogs were valued companions.

Wolf ancestors

Some evidence suggests that several varieties of ancient wolves contributed to the domestic dog, with deliberate or unintentional interbreeding taking traits from one or more of the ancestral wolf lines. Although all wolves belong to the species Canis lupus, there are (or were) many subspecies that had evolved somewhat distinctive appearance, social structure, and other traits. For example, the Japanese wolf, which became extinct in the early 20th century, was much smaller than most wolves, generally had a gray coat with reddish underbelly, and possibly had a more solitary hunting habit; the North American wolf, which still exists in limited ranges, is much larger than many wolf subspecies, displays many coat colors from nearly white through solid black, and exhibits a complex social structure involving highly formulaic dominance and submission rituals.

The Indian or Asian wolf probably led to the development of more breeds of dogs than other subspecies. Many of today's wild dogs, such as the dingo, the dhole and pariah dogs, are descended from this wolf, along with sighthounds such as the Greyhound. Recent genetic evidence (http://www.abc.net.au/rn/science/ss/stories/s728909.htm) shows that most modern dog breeds are related to Asian canines, contradicting earlier hypotheses that the dog, like humans, had evolved originally in Africa. The Asian wolf also likely interbred with descendants of the European wolf to create the Mastiffs—the Tibetan Mastiff being an example of a very ancient breed—leading eventually to the development of such diverse breeds as the Pug, the Saint Bernard, and the Bloodhound.

The European wolf, in turn, may have contributed many of its attributes to the Spitz dog types, most terriers, and many of today's sheepdogs. The Chinese wolf is a probably ancestor to the Pekingese and toy spaniels, although it is also probable that descendants of the Chinese and European wolves encountered each other over the millennia, contributing to many of the oriental toy breeds.

The North American wolf is a direct ancestor to most, if not all, of the North American northern sled dog types; this mixing and crossing still goes on today with dogs living in the Arctic where the attributes of the wolf that enable it to survive in a hostile environment are still valued. Additionally, accidental crossbreeding occurs simply because dogs and wolves live in the same environment. The general reproductive isolation which is required to define dogs and wolves as separate species is purely a result of lack of opportunity, stemming from a general mutual unfamiliarity, suspicion, mistrust, and fear.

The single phenotypic characteristic that seems to separate dogs from wolves is the sickle tail—dogs who have tails all have an upward curve in the tail, whereas wolves' tails hang straight—the "brush tail"—similar to that of a fox.

Speed of domestication

Current research indicates that domestication, or the attributes of a domesticated animal, can occur much more quickly (http://www.amsci.org/amsci/articles/99articles/Trut.html#26879) than previously believed, even within a human generation or two with determined selective breeding. It is also now generally believed that initial domestication was not attained deliberately by human intervention but through natural selection: wild canines who scavenged around human habitation received more food than their more skittish counterparts; those who attacked people or their children were probably killed or driven away, while those more tolerant animals survived, and so on.

Neoteny in the rapid evolution of diverse dog breeds

This rapid evolution of dogs from wolves is an example of neoteny or paedomorphism. As with many species, the young of wolves are more social and less dominant than adults; therefore, the selection for these characteristics, whether deliberate or inadvertent, is more likely to result in a simple retention of juvenile characteristics into adulthood than to generate a complex of independent new changes in behavior. This is true of many domesticated animals, including human beings themselves, who have many characteristics similar to young bonobo. This paedomorphic selection naturally results in a retention of juvenile physical characteristics as well. Compared to wolves, many adult dog breeds retain such juvenile characteristics as soft fuzzy fur, round torsos, large heads and eyes, ears that hang down rather than stand erect, etc.; characteristics which are shared by most juvenile mammals, and therefore generally elicit some degree of protective and nurturing behavior cross-species from most adult mammals, including humans, who term such characteristics "cute" or "appealing".

The example of canine neoteny goes even further, in that the various breeds are differently neotenized according to the type of behavior that was selected.

Breeds that guard flocks, such as the various sheepdog breeds, retain the most juvenile characteristics: they stay close to home with their foster "litter" (which might include a flock of sheep) rather than going out hunting, they have almost no predatory behavior (which would be disastrous in the vicinity of such a natural prey stimulus as sheep), they respond to perceived threats with a lot of vocalization and attempts to alert and engage the dominant individuals in their "pack" (i.e. humans) whenever possible, engaging in actual combat only as a last resort. In addition, they retain very juvenile physical characteristics such as round bodies and heads, soft coats, ears that hang down, and so on, which do not elicit fear responses from the sheep in the way that an appearance similar to that of an adult wolf would. (Compare to the physical appearance of the border collie, a sheep herding dog, whose physical configuration is closer to that of an adult wild canine and who therefore has a greater capacity to frighten sheep into a desired pattern of movement, along with the more adult aggressive temperament to do so).

Breeds that are hunting dogs—that is, pointers, setters, spaniels, retrievers, etc.—have an intermediate degree of paedomorphism; they are at the point where they share in the pack's hunting behavior, but are still in a junior role, not participating in the actual attack. They identify potential prey and freeze into immobility, for instance, but refrain from then stalking the prey as an adult predator would do next; this results in the "pointing" behavior for which such dogs are bred. Similarly, they seize dead or wounded prey and bring it back to the "pack", even though they did not attack it themselves, that is, "retrieving" behavior. Their physical characteristics are closer to that of the mature wild canine than the sheepdog breeds, but they typically do not have erect ears, etc.

Scenthounds maintain an intermediate body type and behavior pattern that causes them to actually pursue prey by tracking their scent, but tend to refrain from actual individual attacks in favor of vocally summoning the pack leaders (in this case, humans) to do the job. This contrasts with sighthounds, who pursue and attack perceived prey on sight, and who maintain the mature canine body type with erect ears, lean bodies, and adult coats.

Terriers similarly have adult aggressive behavior, famously coupled with a lack of juvenile submission, and display correspondingly adult physical features such as erect ears, although many breeds have also been selected for size and sometimes dwarfed legs to enable them to pursue prey in their burrows.

The least paedomorphic behavior pattern may be that of the basenji, bred in Africa to hunt alongside humans almost on a peer basis; this breed is often described as highly independent, neither needing nor appreciating a great deal of human attention or nurturing, often described as "catlike" in its behavior. It too has the body plan of an adult canine predator.

Of course, dogs in general possess a signifcant ability to modify their behavior according to experience, including adapting to the behavior of their "pack leaders"—again, humans. This allows them to be trained to behave in a way that is not specifically the most natural to their breed; nevertheless, the accumulated experience of thousands of years shows that some combinations of nature and nurture are quite daunting, for instance, training whippets to guard flocks of sheep.

Interactions between dogs and humans

The relationship between dogs and humans is ancient. Dogs serve humans in many ways.

For example, a new and particularly effective role of working dogs is that of the drug- or bomb-sniffing dog. All canines have olfactory sensitivity thousands or millions of times more sensitive than humans. This allows them to pick up on the subtle smells of distinctive chemicals, such as cannabis or plastic explosive. Airport security frequently tours concourses and baggage areas with a dog trained to respond to such chemicals.

K-9 police units typically feature a long-term human-canine team, in which the dog is trained to home in on the scents of particular people, and to facilitate their arrest once located. Most criminals find being wrestled to the ground by an aggressive dog much more frightening than being tackled by a human. Such dogs are also frequently used to find missing persons, especially in the wilderness.

Several cities in Italy are experimenting with working dogs as rescue swimmers. In this situation, a strong and well-trained dog is equipped with flotation devices and dropped in the water near a floundering swimmer. The swimmer then grabs onto the dog, and the animal tows the swimmer to shore.
The Newfoundland has long been used for water rescue, not only on shore, but from fishing boats as well.

Dogs are commonly used as search and rescue workers in cases of disasters. The St. Bernard has been historically used for such purposes in Europe in the case of avalanche. In the aftermath of the 9-11 attacks in New York, rescue dogs were brought in to search for survivors in the rubble. Some of the dogs became so disturbed at being unable to find any survivors that people had to be "planted" for the dogs to find so that they did not become depressed at their failure.

Dogs as hunting/sporting partners

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Most dogs are capable of and enjoy swimming, but they should be tested in shallow water first to make sure that they do not panic.

Many people compete with their dogs in a variety of dog sports, including agility, flyball, and many others. This often strengthens the bond between human and dog, since they must trust one another in a variety of environments and must learn how the other works and thinks.

Setters in particular have a long history as upland gun dogs. They have a native ability to discover and "hold" upland game birds; to freeze them momentarily on the ground with their silent, elongated pointing stance. Once the hunter approaches, at his command they will flush the birds to fly and for the hunter to shoot at.

As water dogs, the retrievers are unsurpassed. They can spend long hours in a duck blind and, after the hunter has fired at multiple ducks or geese, they can visually spot and remember the location of downed birds. At command, they dive into the icy water, swim out and retrieve the birds one by one. They can follow hand, verbal, and whistle commands at great distance as the hunter directs them to the downed bird. They typically have large, gentle muzzles to mitigate any potential damage to the game.

When trained, beagles are particularly adept at chasing through thick briars and brush to chase rabbits. Many hound breeds are excellent at treeing raccoons during hunting season.

Hunters with dogs report the satisfaction that the dogs seem to exhibit. Excitement is evident as they see the hunters load weapons, take to the field, and begin the hunt.

Dogs as pets

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A 9 year old English Collie cross. Some say mongrels make the best pets

Relationships between humans and dogs are often characterized by strong emotional bonds. Consequently, dogs are popular as pets and companions, independent of any utilitarian considerations. Many dog owners consider having unconditional acceptance from a friend who is always happy to see them to be quite utilitarian, particularly if the dog also leads them to regular exercise. Empirically, dogs are quite dependent on human companionship and may suffer poor health in its absence.

Some research demonstrates that dogs are able to convey a depth of emotion not seen to the same extent in any other animal; this is purportedly due to their closely-knit development with modern man, and the survival-benefits of such communication as dogs became more dependent on humans for sustenance.

Nevertheless, it is often unwise to anthropomorphize the responses of dogs. Despite understandably positive interpretations by dog owners, it is questionable whether these animals are truly capable of feeling emotions on a human level. More research is needed to determine the intelligence level of dogs, and the motivations behind their responses to their masters.

Dogs as food

In some places dogs are raised for their meat, causing friction with people who keep dogs as pets. In times of great stress, such as when the Vikings of Greenland starved to death at the start of the Little Ice Age (14th century - 19th century), humans have been known to eat their pets.

Dog society

Dogs thrive in small social groups or packs which, from their viewpoint, includes humans.

Dog breeds

There are numerous dog breeds, over 800 being recognized by various kennel clubs worldwide. As all dog breeds have been derived from mixed-breed dog populations, the term "purebred" has meaning only with respect to a certain number of generations. Moreover, many dogs, especially outside the United States and Western Europe, belong to no recognized breed.

A few basic breed types have evolved gradually during the domesticated dog's relationship with man over the last 10,000 or more years, but most modern breeds are of relatively recent derivation. Many of these are the product of a deliberate process of artificial selection. Because of this, some breeds are highly specialized, and there is extraordinary morphological diversity across different breeds. Despite these differences, dogs are able to distinguish dogs from other kinds of animal.

The definition of a dog breed is a matter of some controversy. Some groups use a definition that ultimately requires extreme in-breeding to qualify. Dogs that are bred in this manner often end up with severe health problems. Other reorganizations define a breed more loosely, such that an individual may be considered of one breed as long as, say, three of its grandparents were of that breed. These considerations come into play among breeders who enter their dogs in dog shows. Purebred dogs frequently suffer from serious inherited health and/or behavioral problems. This is by no means true of the majority of purebred dogs, and the same problems can occur in populations of mixed breed dogs. Even prize-winning purebred dogs are sometimes possessed of crippling genetic defects due to inbreeding.

In February2004, the Canine Studies Institute in Aurora, Ohio, managed to arrange all breeds of dog into ten categories, according to Darwinianevolutionary principles. [1] (http://news.independent.co.uk/world/science_medical/story.jsp?story=491197)

The behavior and appearance of a dog of a particular breed can be predicted fairly accurately, while mixed-breed dogs show a broader range of innovative appearance and behavior.

Mixed-breed dogs are dogs that do not belong to specific breeds, being mixtures of two or more. Mixed breeds, or dogs with no purebred ancestry, are not inherently "better" or "worse" than purebred dogs as companions, pets, working dogs, or competitors in dog sports. Sometimes mixed-breed dogs are deliberately bred, for example, the Cockapoo, a mixture of Cocker Spaniel and Miniature Poodle. Such deliberate crosses may display hybrid vigor and other desirable traits, but can also lack one or more of the desired traits of their parents, such as temperament or a particular color or coat. However, without genetic testing of the parents, the crosses can sometimes end up inheriting genetic defects that occur in both parental breeds. Deliberately crossing two or more breeds is also a manner of establishing new breeds.

Dog reproduction

As with most domesticated species, one of the first and strongest effects seen from selective breeding is, logically enough, selection for cooperation with the breeding process as directed by humans. In dogs, this takes the form of abolition of the pair bonding seen in wild canines, as well as the ability of female domestic dogs to come into estrus (also called in season or in heat) at any time of the year and usually twice a year; unlike undomesticated canine species where the females typically come into once season a year, usually in late winter, and bear one litter of young. Most bitches come into season for the first time between 6 and 12 months, although some larger breeds delay until as late as 2 years. Like most mammals, the age that a bitch first comes into season is mostly a function of her current body weight as a proportion of her body weight when fully mature, rather than age, with the different maturation rates of the various sizes of dogs accounting for this variation in age of first season. The amount of time between cycles varies greatly among different dogs, but a given dog's cycle tends to be consistent through her life. Dogs bear their litters roughly 9 weeks after insemination.

An average litter consists of about six puppies, especially for breeds that have not strayed too far from their wild ancestors. However, litters of many more or only one or two puppies are also common. Some breeds have a tendency to produce very large litters. Since a mother can provide milk for only a few of those puppies, humans must assist in the care and feeding when the litter exceeds eight or so.

Some breeds have been developed to emphasize certain physical traits beyond the point at which they can safely bear litters on their own. For example, the Bulldog often requires artificial insemination and almost always requires cesarean section for giving birth.

Puppies often have characteristics that do not last beyond early puppyhood. For example, eyes are often blue when they first open but change to other colors as the puppy matures. As another example, Kerry Blue Terrier puppies have black coats when they are born and their distinctive "blue" color appears gradually as the puppy nears maturity. The ears of erect-eared breeds such as the German Shepherd Dog are softly folded at birth but straighten as the puppy grows; in cases where they fail to straighten on their own, owners sometimes opt for surgical intervention.

Dog experts advise that dogs not intended for further breeding should be spayed or neutered so that they do not have undesired puppies, which are often abandoned. Abandoned dogs who go feral are particularly dangerous; they lack the skills of wild canines at survival in the wild, as well as the genetic and learned fear of humans that keeps wild canines away from humans and their possessions, so they form predatory packs that attack livestock and occasionally also prove dangerous to humans. The overpopulation of unwanted dogs is so great that almost all dogs who end up in animal shelters are euthanized due to lack of space and resources. Spaying and neutering can also help prevent hormone-driven diseases such as breast cancer and prostate cancer, as well as undesired hormone-driven behaviors. Contrary to myth, it is not required for a female dog to either experience a heat cycle or have puppies before spaying, and likewise, a male dog does not need the experience of mating before neutering; these myths are responsible for numerous unnecessary health problems and unwanted puppies. Attempts by owners to carry on some particular admirable qualities of their dogs by breeding them usually fail. Dogs of mixed breed do not "breed true"; i.e., with a mixed breed dog the offspring may not carry characteristics found in a parent, or even shared by both parents. Similarly, but to a lesser extent, even with purebreed dogs sold as pets the offspring may not have the subtle best qualities of the parents; it may be necessary to go back to the high quality breeding stock and reproduce the original mating as closely as possible to reproduce the desired characteristics very closely. Of course, most owners who let their dogs reproduce will feel the offspring are superior; however, realistically speaking, the natural sentimental bias makes it just as likely that they would feel the same way about any dog they acquired, from the pound or elsewhere.

Dangers

As evidenced by their attacks on other creatures, both wild and domestic, dogs can be aggressive predators. Their sharp teeth and powerful jaws can inflict serious injuries; their sharp claws have powerful muscles behind them. Scratches from dogs are easily infected. Even without aggressive intent, by just acting boisterous, a dog of adequate size can knock a person down, with the risk of serious injury. It has been observed that any dog should be regarded as the equivalent of a child, who happens to be armed with a deadly weapon. Formal and informal training, selective breeding, and society's response to a dog who proves dangerous combine to reduce the overall physical threat from dogs to a very low level; however, although confrontations between man and dog ordinarily stop well short of harm, improperly managed confrontations can lead to severe injury from even the most well-tempered dog, much as almost any human could be incited to violence given sufficiently serious provocation.

Contrary to myth, barking dogs can bite a person who fails to recognize the warning. Likewise, a wagging tail indicates an excited state, which is not always a result of "happy" excitation; a wagging dog is not equivalent to a purring cat. A highly disturbed dog may sometimes emit confusing or misleading signals, much as the development of anger or an aggressive mood in a human being may not always be externally obvious.

Human behavior as provocations

Some human behavior (especially people unfamiliar with dogs) can potentially evoke a predatory or aggressive response from a dog. These include (but are not limited to):

Attacking a dog or its companions, canine or human, or acting in a manner that the dog perceives as an attack (for example, a sudden enthusiastic hug)

Attempting to take food away from a dog, or moving towards a dog's food or between a dog and its food, even inadvertently

Threatening a puppy in the presence of an adult dog, especially its mother

Looking a dog directly in the eyes, especially when on the same level of the dog (such as small children), especially a dog who is not familiar with you

Approaching a sick or injured dog. Note that older dogs, like people, often seem to become "cranky" as they accumulate aches and pains, and develop a tendency to become "snappish"

Related to the previous point, failure to recognize a dog showing signs of insecurity or fear and continuing whatever behavior is causing the dog's anxiety to increase, until "fear biting" occurs. Again, an older or chronically infirm dog is liable to develop feelings of vulnerability and anxiety, and therefore become less tolerant and more aggressive

Running away from a dog: the chase-and-catch instinct inherited from wolves is not fully lost, and most dogs can outrun and overtake the average human. Similarly, the natural instinct to jerk one's hands upwards away from an inquisitive dog often elicits in the dog a strong impulse to grab and hold, or at least to investigate, resulting in the dog jumping on the person and thrusting its head towards the raised hands

"Sudden" aggressiveness

It is also of note that, rarely, some dogs with no prior signs of aggressiveness or any exposure to stimuli that might generate aggression seem to suddenly develop a physically aggressive streak. The first such attack is often dismissed as a fluke (triggered by one of the factors above, for instance) in view of the dog's benign history, but when a few unprovoked attacks occur within a relatively short span of time, the dog is generally recognized as dangerous. Similarly, some dogs seem, for no apparent reason, to become unreasoningly aggressive when triggered by a particular stimulus, for instance a touch on a specific region of the body which does not seem to be painful (distinct from the more understandable reaction when a painful area is stimulated), even though nothing in the dog's history would have trained it to react in such a fashion. While we cannot understand what is happening from the dog's point of view, the existence of such behaviors in a few dogs is sometimes considered in reference to the question of whether criminal, antisocial, violent, or other pathological behavior in human beings can sometimes be innate.

Background for aggression

Although most dogs are not inherently aggressive (unless they are feral, trained to attack intruders, threatened, or provoked), it is important to remember that they are predatory by nature and instinct is something that never disappears. This is not to say that all of the above behaviors will always result in injury. In fact, dog experts advocate acclimating a puppy to provocative situations such as removal of its food or sudden movements by a stranger when its behavior can be controlled to train it to restrain its aggressive impulses even more thoroughly, so that later in life, similar situations can be dealt with without danger; for instance if the dog is found eating something dangerous, or is wounded and needs to be transported for medical attention.

Small children are especially prone to provoking dogs, in part because their size and movements suggest similarities to prey that dogs instinctively attack, rather than adult humans to whom the dog has learned to submit. Also, young children may well unintentionally provoke the dog (pulling on ears or tails is common, as is surprising a sleeping dog) because they do not know any better. Because of a dog's pack instincts, more dominant dogs may view children or even adults as rivals rather than as superiors, and attempt to establish dominance by physical means; any examples of such behavior, no matter how tentative, should be extremely firmly discouraged as early as possible, to deliver to the dog the message that all humans are to be regarded as superiors. To avoid potential conflicts, even reliably well-behaved children and dogs should not be allowed to interact in the absence of adult supervision until both have absolutely demonstrated their ability to always behave appropriately towards each other, no matter what the situation.

Dogs with strong chase instincts may also fixate on specific stimuli, such as a fast-moving, brightly colored running or cycling shoe, as a prey object, and not recognize the whole picture as a human being; this is probably operative in the majority of cases of otherwise nonaggressive dogs chasing cyclists and runners. In these cases, if the individual stops, to the dog it is as if its prey suddenly disappears and is replaced by a human, and it immediately loses interest. Of course, this should not be confused with cases of actual aggressive dogs who might take the opportunity to attack. Similarly, while most dogs who bark aggressively at strangers, particularly when not on "their" territory, will flee if the stranger "calls its bluff" and replies with a mock aggressive move, there is always the danger of the occasional dog who will stand its ground and further escalate the situation.

Miscellaneous facts

Treats

Many dogs consider anything given them directly by hand to be a treat, even the food they are accustomed to at meal time. Special dog treats are not necessary for such animals. Care should also be taken to avoid dropping small but inedible objects (such as marbles, coins, engagement rings, etc.) around such dogs.

If a dog has something valuable (rings, money, irreplaceable items), a treat should be used to "barter" with the dog to retrieve the stolen item. Chasing a dog will encourage play behavior, which may cause the item to be swallowed or destroyed.

Dogs and the Zodiac

The Dog is one of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. It is thought that each animal is associated with certain personality traits. See: Dog (Zodiac).

Dogs and temperature regulation

A common misconception is that dogs do not sweat. Primarily, dogs regulate their body temperature in a completely different way, through their tongue. That is why after a dog has been running or on a hot day you will see its mouth wide open and tongue hanging out. This is a very efficient form of cooling in terms of maximizing heat lost while conserving moisture, because it carries heat from the hottest part of the body, the interior core of the thorax, compared to sweating, which cools the already coolest part of the body, the skin. Besides being intuitively correct, this higher efficiency of thermal loss in terms of moisture conservation stems from heat flow being proportional to temperature gradient in a given system. In addition, dogs effectively sweat through the pads of their feet, since they are not furred. Again, on a warm day and after exercise, a dog's naturally wet footprints might be visible on a smooth floor.

Dogs possess a rete mirabile in the carotid sinus at the base of their neck, a complex of intermingled small arteries and veins which acts as a heat exchanger to thermally isolate the head, containing the brain, the most temperature sensitive organ, from the body, containing the muscles, where most of the heat is generated. The net result is that dogs can sustain a high degree of physical exertion over a prolonged time in a hot environment, compared to animals which lack this apparatus; thus, a dog chasing a jackrabbit through the desert may not be able to outrun the rabbit, but it can continue the chase until the rabbit literally drops dead from overheating.

A fine sense of direction

It has been observed that a lost dog can often find its way home, sometimes traveling over long distances. It is believed that dogs and cats know the correct position of the sun at their homes. When lost, the animal notes the angle of the sun as it travels, and moves in the direction that indicates that the angle is becoming correct.

Diseases and ailments

Some diseases, ailments, and poisons are common to both humans and dogs; others are different.

Transferable diseases

Most diseases that affect dogs or humans are not transferable between the two species. There are some exceptions:

Rabies, or Hydrophobia, is a usually fatal disease which can be transmitted to dogs or humans by the bite of many mammals, including dogs, cats, raccoons, and bats. Although rodents and similar small mammals can be infected with the disease artificially, they are generally not found infected in the wild; the current hypothesis is that they are not likely to survive any attack which would infect them. Animals with rabies suffer deterioration of the brain and tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease. Areas which are rabies-free, (usually islands) such as Britain, Australia or the U.S. state of Hawaii, have strict quarantine laws to keep their territories rabies-free requiring long periods of isolation and observation of the animal, which make it very unattractive in practice to move there with a pet unless it is quite young. Areas which are not rabies-free usually require that dogs (and often cats) be vaccinated against rabies. A person or dog bitten by an unknown or unvaccinated dog (or other animal) should always be treated without waiting for symptoms, given the potentially fatal consequences if the biter was rabid; there has only been one case in history of someone surviving rabies when treatment was not begun until after symptoms appeared. The biter should be apprehended if at all possible, as only euthanasia and autopsy of the brain can determine if it was rabid. This should be a great incentive to dogowners to vaccinate their dogs even if they feel the risk of their dog contracting rabies is low, since vaccination will eliminate the need for their dog to be euthanized and examined in this fashion should it bite anyone or be suspected of biting anyone, as well as the need for it to be treated for rabies if it is suspected of being bitten.

Parasites, particularly intestinal worms such as hookworms, tapeworms and roundworms, can be transmitted in a dog's saliva or feces. Some have fleas as intermediate hosts; the worm egg must be consumed by a flea to hatch, then the infected flea must be ingested (usually by the dog while grooming itself, but occasionally by a human through various means) for the adult worm to establish itself in the intestines. The worm's eggs then pass through the intestines and adhere to the nether regions of the dog, and the cycle begins again.

Fleas and ticks of various species can be acquired and brought home by the dog where they can multiply and attack humans (as well as vice versa). This is particularly important, now that tick-borne Lyme Disease has become endemic throughout a large area, in addition to other similar diseases such as Rocky Mountain Spotted Fever. Although dogs do not seem to be as susceptible to such diseases as humans, similar rickettsial diseases have been spread by dogs to humans through such mechanisms as a dog killing an infected rabbit, then shaking itself off in the house near enough to its owners to fatally infect most of the family.

Leptospirosis is a bacterial disease that affects humans and animals. It is caused by bacteria of the genus Leptospira. Humans and dogs become infected through contact with water, food, or soil containing urine from infected animals. This may happen by swallowing contaminated food or water or through skin contact, especially with mucosal surfaces, such as the eyes or nose, or with broken skin.

Genetic ailments

Genetic conditions are a problem in some dogs, particularly purebreeds:

Dangerous foods

Some foods commonly enjoyed by humans are dangerous to dogs:

Dogs love the flavor of chocolate, but chocolate in sufficient doses is lethally toxic to dogs (and horses and possibly cats). Chocolate contains theobromine, a chemical stimulant that, together with caffeine and theophylline, belongs to the group of methylxanthinealkaloids. Dogs are unable to metabolize theobromine effectively. If they eat chocolate, the theobromine can remain in their bloodstreams for up to 20 hours, and these animals may experience fast heart rate, hallucinations, severe diarrhea, epileptic seizures, heart attacks, internal bleeding, and eventually death. A chocolate candy bar can be sufficient to make a small dog extremely ill or even kill it. Approximately thirty grams of baking chocolate per kilogram (1/2 ounce per pound) of body weight is enough to be poisonous. In case of accidental intake of chocolate by especially a smaller dog, contact a veterinarian or animal poison control immediately; it is commonly recommended to induce vomiting within two hours of ingestion. Large breeds are less susceptible to chocolate poisoning, but still are far less tolerant of the substance than humans are.

Note:Carob treats are often available as dog treats; these are unrelated to chocolate and are safe.

It has recently been confirmed that grapes and raisins can cause acute renal failure in dogs. The exact mechanism is not known, nor any means to determine the susceptibility of an individual dog. While as little as one raisin can be fatal to a susceptible ten pound dog, many other dogs have eaten as much as a pound of grapes or raisins at a time without ill effects. The dog usually vomits a few hours after consumption and begins showing signs of renal failure three to five days later.

Onions and to a significantly lesser extent garlic contain thiosulfate which causes hemolytic anemia in dogs (and cats). Thiosulfate levels are not affected by cooking or processing. Small puppies have died of hemolytic anemia after being fed baby food containing onion powder. Occasional exposure to small amounts is usually not a problem, but continuous exposure to even small amounts can be a serious threat.

Macadamia nuts can cause stiffness, tremors, hyperthermia, and abdominal pain. The exact mechanism is not known. Most dogs recover with supportive care when the source of exposure is removed.

Alcoholic beverages pose much the same temptation and hazard to dogs as to humans. A drunk dog displays behavior pretty much analogous to that of an intoxicated person. (However, beer presents another problem; see below.)

Hops, the plant used to make common beer, can cause malignant hyperthermia in dogs, usually with fatal results. Certain breeds, such as Greyhounds, seem particularly sensitive to hop toxicity, but hops should be kept away from all dogs. Even small amounts of hops can trigger a potentially deadly reaction, even if the hops are "spent" after use in brewing.

Some dogs have food allergies much as humans do; this is particular to the dog and not characteristic of the species as a whole. An example is a dog vomiting whenever he eats salmon; many humans likewise have seafood allergies.

Common unsafe consumption

Many dogs have a fondness for feline feces (which, due to the feline digestive system, are high in protein and consumed by many animals in the wild), and will raid a kitty litter box for "treats" (coprophagia). This can be unsafe for the dog's health if the cat has any diseases.

Feeding table scraps to a dog is generally not recommended, at least in excess. Dogs get ample correct nutrition from prepared dogfood. Otherwise, just as in humans, their diet must consist of the appropriate mix of vegetables, carbohydrates, and proteins, with the appropriate mix to provide all of the minerals and vitamins that they need. A human diet is not ideal for a dog; in addition, the scraps often consist of fat rather than meat protein, which is no better for dogs than it is for humans. Lastly, many people overfeed their dogs by giving them all the table scraps that the dogs will eat—which is usually all the table scraps they are fed, which is often too much food. The result of too much food is obesity, an increasingly common problem in dogs, which can cause numerous health problems just as it can in humans, although dogs are much less susceptible to the common cardiac and arterial consequences of obesity than humans are.

Common household chemicals

Some common household chemicals are particularly dangerous to dogs:

Antifreeze, due to its sweet taste, poses an extreme danger of poisoning to a dog (or cat) that either drinks from a spill or licks it off its fur. The antifreeze itself is not toxic, but is metabolized in the liver to a compound which causes kidney failure, and eventual seizures and death. By the time symptoms are observed, the kidneys are usually too damaged for the dog to survive. Treatment for a dog which has recently consumed antifreeze is to dose the dog with large quantities of ethanol, which occupies the enzymes in the dog's liver, long enough for the unmetabolized antifreeze to be passed out harmlessly through the kidneys. Dogs should not be allowed access to any place in which an antifreeze leak or spill has happened until the spill is completely cleaned out. Some brands of antifreeze are marketed as being less harmful or less attractive to animals.

Additional health information

Dogs are susceptible to various diseases; similarly to humans, they can have diabetes, epilepsy, cancer, or arthritis. Other diseases are more specific to canines.

Breeds with deep chests and narrow waists, such as the Bouvier des Flandres or Doberman Pinscher, for instance, are susceptible to a syndrome of gastric torsion and bloat, where the stomach twists on its supporting ligaments, sealing off the exits, and the contents begin to generate gas pressure which is not only terribly painful (as can be imagined by anyone who has experienced even mild gas pains), but kills large areas of stomach tissue fairly quickly, resulting in a painful death within a very few hours. A similar disease is seen in cattle and horses; and a similar home remedy has sometimes been effective when a veterinarian is not at hand, i.e. puncturing the stomach from outside with a sharp object to relieve the pressure. Obviously, such a remedy must only be attempted as a last resort. Dogs who have experienced such an attack are very susceptible to another which is usually more severe, and this is one case where the most medical intervention usually proves the best choice, normally involving abdominal surgery to tack the dog's stomach down in several places to prevent recurrence.

Elderly dogs are susceptible to an unusual form of intense vertigo, the cause of which is unknown; the affected dog is unable to stand up and remains sprawled on the floor, the eyes displaying intense nystagmus, for typically a few days. While terrifying in appearance, owners often fearing that the dog has had a fatal stroke (which is actually uncommon in dogs), the vertigo passes within a few days and by the end of a week the dog is staggering around upright, and within another week there is no evidence that anything at all had happened. The only risk of the disease is that the dog is unable to eat or drink in that condition, and must receive supportive therapy of intravenous fluids and nutrition; a light sedative is usually also administered, as the dog naturally seems terrified during the experience.

A serious risk to dogs is heartworm; as the name suggests, an infected mosquito injects a larva into the dog's circulatory system which takes up residence in the heart, consuming cardiac muscle while growing and reproducing to an alarming degree. The effects on the dog are quite predictable, cardiac failure over a year or two, leading to death. Treatment of an infected dog is difficult, involving an attempt to poison the healthy worm with arsenic compounds without killing the weakened dog, and frequently does not succeed. Prevention is much the better course, via heartworm pills which are fed to the dog and contain a compound which kills the larvae immediately upon infection without harming the dog. Unfortunately, the pills tend to be unpalatable to the dog. Often they are available combined with other parasite preventives.

Intelligence

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Dogs can be trained to retrieve

Among dog lovers, dogs are generally valued for their intelligence. Anecdotal evidence suggests that dogs have a reasonably high intelligence. For a detailed discussion on what dog intelligence is, see dog intelligence.